Telephone trunk-line system



(No Model.)

J. I. SABIN & W. HAMPTON; TELEPHONE TRUNK LINE SYSTEM.

Patented May 22, 1894.

i; Q a .2 mm

H g a UNITED STATES PAT NT OFFICE.

JOHN I. SABIN AND WILLIAM HAMPTON, OF SAN FRANCISCO, CALIFORNIA.

TELEPHONE TRUNK-LINE SYSTEM.

SPECIFICATION forming part Of Letters Patent No. 520,083, dated May 22,1894- Application fil February 12, 1894. Eerial No. 499,954. (No model.)

Our invention relates to a telephone trunk line system, and its objectis to facilitate the connection of subscribers through trunk lines, andto simplify the operators connecting apparatus.

Our invention, in its preferred form, comprises telephone linesextending to the 'operators boards, and terminating each in the contactterminals of a plug mounted upon a flexible cord. In a shunt circuit islocated the subscribers individual indicator which is of theself-restoring type, a battery being located in the shunt circuitadapted to be opened or closed through the indicator by a switch at thesubscribers station, which switch may be the subscribers telephoneswitch. The shunt circuit is permanently connected with the line, sothat the indicator may serve both as a clearing out and as a callingindicator. eral boards are connected by independent telephone circuits,each operator being also provided with a telephone set terminating insockets upon the board whereby she may connect herself in circuit with acalling subscriber by the insertion therein of the plug of his line. Theseveral boards are connected by a series of trunk lines terminating inswitches, into which the plugs of the subscribers may be inserted toconnect them in circuit. In connecting with the trunk line, the plug ofthe calling subscriber is removed from the socket of the operatorstelephone set and placed in the trunk line switch, the operator beingthus unable to cut her telephone set into circuit without breaking thetalking circuit, absolute secrecy between the conversing subscribersbeing thus secured.

The operator at the board of the called subscriber may ring over thecalled subscribers line by touching the shell of such subscribers Theoperators at the sevplug, before inserting the same in the switchsocket, to a bar grounded through the genhook a, to connect the groundbranch containing the bell a with one limb of the line, the hook whenthe telephone receiver is in use closing the circuit through thetelephone set and cutting from circuit the branch containing the bell.The limbs a a of the line of subscriber A extend to the first operatorsboard, where they terminate respectively in the tip and the sleeve of aplug a Ina shunt circuit a is included the individual indicator atogether with a battery a". To balance the line a retardation coil (1.may be employed. Likewise, the limbs b b of the line of subscriber B,extend to a second operators board, terminating thereat in the terminalsof the single cord plug 1), a battery 6 and indicator 1) being includedin a shunt circuit If. The boards of the operators are connected by anumber of trunk lines, but one of which, a, is

shown in the drawing, the lines terminating.

at the boards in line springs c c and c 0. The boards are alsoconnected, in the usual manner, by a local telephone circuit 0 by meansof which the operators may converse. The operators telephone sets cl (1'terminate respectively in the line springs (Z (Z and d d of thetelephone sockets d and (P. The operators are also provided with ringingplates e e connected through generators e e to ground. The operators arefurther provided with battery plugs f f connected through batteries f fto ground. In the shell limb of the trunk line is provided a condenser gfor a purpose hereinafter to be described.

Instead of providing a generator ringing plate and a battery plug asingle generator or battery plug may be providedagainst which the plugof the called subscriber may be placed in the first instance to send theringing current, and which may be lifted into contact with the shell ofthe plug after it has been placed in the trunk line socket, for thepurpose of sending an additional calling signal, but We prefer theprovision of a ringing bar and a battery plug. Y

lVe will now describe the operation of the system as above described.Supposing subscriber A desirous of speaking with subscriber B, whosenumber may be 874; he removes his telephone from its hook, thus closingcircuit of battery a and actuating indicator a and informing theoperator that he desires connection. The operator then inserts plug (1,of subscriberAin her telephone socket (1 Her telephone set being now incircuit, she inquires the number of the called subscriber. Havingreceived the number of the called subscriber the operator at the firstboard merely repeats to the operator at the second board, through thelocal telephone circuit c the number of the called subscriber, 874, uponhearing which the operator at the second board instructs the firstoperator which trunk line to use by repeating the nu mber of the trunkline. Supposing the second operator to say on 14, the operator at thefirst board removes plug a from socket d and inserts it in the socket oftrunk line 14..

The operator at the second board upon retion of indicatorb since hecloses the circuit of battery I) by removing his telephone. Should B notrespond immediately, the operator may send another ringing current bytouching her ringing plugf to the shell of b as it rests in the socket,the current of the battery being prevented from passing toward thecalling subscribers station by means of condenser 9. When thesubscribers have completed conversation and have hung up theirtelephones, the operators will be informed of the fact by the indicatorsa and b and will remove plugs a and b from thesockets of the trunk line.The condenser g renders the indicators individual to the two connectedsubscribers by preventing the indicator battery of one subscriber fromaffecting the indicator of the other subscriber.

lVe are aware that our invention is susceptible of modifications, andthat features of our invention may be used in other connections, and wedo not, therefore, desire to limit ourselves to the specific embodimentshown and described herein, but

We claim as new and desire to secure by Letters Patent 1. Thecombination with two single cord telephone lines connected forconversation through the central station, of individual indicators andbatteries located in closed bridges between the sides of each of saidlines, and a. condenser inone side of the circuit and between saidbridges, whereby said individual indicators may serve as individualclearing out indicators, substantially as described.

2. In a trunk line telephone system, the combination with telephonelines terminating in the contacts of connecting plugs at the operatorsboards, of batteries and individual indicators located in permanentbridges between the opposite sides of each of said lines, trunk linesterminating in switch sockets at the several boards, and a condenser inone of the limbs of each of said trunk lines where by connection may bemade by the insertion of the subscribers plugs in the trunk linesockets, and the individual indicators may serve for clearing outindicators, substantially as described.

3. In a trunk line telephone system, the combination with telephonelines terminating in the contacts of connecting plugs at the operatorsboards, of batteries and individual indicators located in permanentbridges between the opposite sides of each of said lines, and trunklines terminatingin switch sockets at the several boards, and acondenser in one limb of said trunk line, whereby the individual callingindicators may serve as individual clearing out indicators,substantially as described.

4. The combination with asingle cord telephone line, of an operatorstelephone apparatus terminating in a switch socket, whereby theoperators telephone circuit may be "brought into circuit by theinsertion of the subscribers plug, substantially as described.

5. The combination with a trunk line terminating in a switch socket atthe operators board, of single cord telephone lines terminating inconnecting plugs thereat, and an operators telephone set terminating ina switch socket, substantially as described.

6. The combination with a metallic circuit telephone line terminating ina cord and plug at the central station, of a calling device in anormally closed ground from one limb of the line, and a stationary plateat the central station connected through a source of calling currents toground; whereby said calling device may be actuated by touching saidplug to said stationary plate, substantially as described.

In witness whereof we hereunto subscribe our names this 5th day ofFebruary, A. D. 189 4.

J OHN- I. SABIN. \VILLIAM HAMPTON. lVitnesses:

F. F. SPRING R, J. H. CoRooRAN.

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